The ongoing market trend to involve semiconductor devices in new applications continues to strive for reductions of physical device size while simultaneously requiring enhanced device performance. This market pressure holds for active semiconductor devices as well as for passive components and for systems combining active and passive elements. Passive components include inductors, coils, resistors and capacitors. Among the passive components of electronic systems are capacitors of various sizes. To save real estate of a system and reduce parasitics, capacitors are fabricated in small size by using thin metal electrodes and thin dielectric materials and are often placed as piece parts in tight proximity to other system components, such as transistors and inductors. To further conserve system real estate and minimize parasitic electrical effects, these components are sometimes placed under or on top of other components. For example discrete capacitors are sometimes placed on top of other components.
Electronics systems include power supply devices for converting one DC voltage to another DC voltage. The converters include switching converters where power transistors are turned on and off at a frequency of up to several MHz. The on time is determined by using pulse width modulation at the gate terminal of a transistor coupled between a power source and a switching node, which is coupled to an output terminal through resonant circuit using a capacitor and inductor to smooth the ripple from the output voltage. For many power switching devices, the integrated circuit (IC) that includes the power metal oxide semiconductor field effect transistors (MOSFETs), and a gate driver IC and a controller IC are assembled as individual components. The ICs are typically attached to a rectangular or square-shaped pad of a metallic leadframe; the pad is surrounded by leads that form output terminals. This approach consumes area and increases the footprint of the module. In another recently introduced scheme, the control IC and the driver IC are assembled vertically on top of the other as a stack. In this assembly, at least one MOSFET IC can be configured for vertical current flow; the source electrode of the control IC is facing the drain electrode of the driver IC.
Stacked chip (a “chip” is a semiconductor die) power MOSFETs have been proposed that integrate a capacitor into a package of the system. To increase the obtainable value of capacitance per area by at least one order of magnitude, capacitors have recently been demonstrated based on the concept of folding the third dimension into the area of two dimensions: cavities are etched into metal boards made, for example, of aluminum; the aluminum surface in the cavities is then oxidized, and the cavities are filled with a conductive material such as a polymeric compound. The three-dimensional structure, or body, thus formed may obtain contacts, or electrodes, to the metal board and the conductive polymeric compound, and can be operated as a capacitor offering high capacitance values. These capacitors are referred to as nanoparticle capacitors.
However, especially when the passive components are nanoparticle capacitors made with thin parallel electrodes and with a thin body between the electrodes, these discrete capacitors are difficult to integrate into the packages of the system, since elaborate via or vertical interconnection processes are needed to reach both of the parallel electrodes of the capacitors. Among the methods employed are conductive vertical attachment materials such as epoxies and solders, vertical vias drilled through the capacitor layers, and substrates with vertical interconnects; however, these methods are cumbersome and expensive.